Question

So I want to create a very simple structure out of group and locator nodes in Maya which will then be exported for use in my game level.

e.g.

Group_Root
  group_parent
    - group1
      - locator1
    - group2
      - locator2
    - group3

There is only one Group_Root in the file, there are many group_parents ( each uniquely named ) However all group_parent s have the same three sub-group names( "group1", "group2", "group3" ) and all group1 have a locator called locator1

What I have so far is:

group_parent = c.group( em=True, name="group_parent", parent="Group_Root")
modes =  ["group1", "group2", "group3"]
for mode in modes:
    mode_group = c.group( em=True, n=mode, parent=group_parent )
    if mode == "group1":
            s = c.spaceLocator(name="locator1")
            c.parent( mode_group ) 
    elif mode == "group3":
            s = c.spaceLocator(name="locator2")
            c.parent( mode_group )

However I get this error at "c.parent(mode_group)"

# Error: Object group1 is invalid

Presumably because there are more than one node called "group1" so it doesn t know which one to parent.

Any idea how I do this with full paths? e.g. "Group_Root|group_parent|group1"

Answer 1

Have you seen VFX Overflow? It s Q&A for visual effects, so I d expect a number of the watchers to be quite familiar with Maya/MEL and Python. That said, it is fairly new so the user base is still small...

Answer 2

Names can be a bit annoying with MEL. In general, it s good practice to never trust a name to be what you re specifying.

This is a good example of how *not to do things:

group -n myGroup1 circle1 sphere1;

..because that is in no way guaranteed to result in something named "group1". The better way to do it is to run your command and capture the result in a string variable, such as:

string $result = `group -n myGroup circle1 sphere1`;

Then, use $result to refer to the resulting group. That will still work, even if the group ended up being called myGroup23 .

I m not sure how the above looks in Python, as I m mainly familiar with straight MEL, but the same principles should apply.

Another thing to look at is the namespace functionality (namespace and namespaceInfo), which could be used to define a new namespace for the unique, top-leve group at hand.

Hope that helps

Answer 3

I m guessing that it being over two years, you ve figured this one out by now.. but for posterity, there were two issues - firstly, you were spot on with the need for absolute paths, but there was also a slight bug in the way you were applying the maya.cmds.parent() call. I ve just done some light rewriting to illustrate - mainly you could use the fact that when you create things they become selected by default, and maya.cmds.ls() is smart enough to return you what you need.. Ergo:

c.group( em=True, name="group_parent", parent="Group_Root")
group_parent = c.ls(sl=True)[0]

modes =  ["group1" , "group2", "group3"]
for mode in modes:
    c.group( em=True, n=mode, parent=group_parent )
    mode_group = c.ls(sl=True)[0]
    if mode == "group1":
            c.spaceLocator(name="locator1")
            s = c.ls(sl=True)[0]
            # maya.cmds.parent() with something selected will actually
            # parent the specified object to the selected object. 
            # You don t want that.


            # We might as well use the explicit syntax to be sure 
            # (parent everything specified to the last item in the list)
            c.parent( s, mode_group ) 
    elif mode == "group3":
            c.spaceLocator(name="locator2")
            s = c.ls(sl=True)[0]
            c.parent( s, mode_group )

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